The test and examination of objects such as fabricated structures and processed materials, without damaging them, is now of immense importance in a wide range of industrial situations. The benefits obtained by inspecting the physical condition of an object to ensure that it meets its specifications are well known to manufacturers. Perhaps, most notable among these benefits are the improved efficiency and product quality gained by preventing the use of non-conforming material in a manufacturing process. Cylindrical structures, such as pipes and rods, and non-cylindrical materials, such as cast bars, comprise a large population of these objects.
Perhaps the most widely used NDT/NDI material inspection methodologies today utilize ultrasound (UT) and eddy current (EC) probes, both of which include single element and/or array probes. They are used to detect and characterize static defects or anomalies in metal, non-metal, or fiber composite structures in conjunction with rapid manufacturing processes.
One of the most difficult challenges encountered when inspecting these materials arises from the fact that the orientation of defects is typically unknown prior to inspection. Accordingly, conventional inspection probe systems are capable of scanning the test object at a plurality of incident inspection angles—such as, longitudinal, transverse, normal and oblique. This requirement for complex multi-angle inspection places a significant burden on system design, manufacturing, and maintenance.
The present disclosure is primarily concerned with two types of NDT/NDI systems that are commonly referred to as ‘pipe’ (or test object) and ‘bar’ inspection systems, such as the ones provided by the assignee of the present disclosure, i.e., the Olympus-NDT company. Furthermore, the present disclosure primarily describes exemplary inspection methodologies that employ phased-array or single element UT probes; however, it is not limited in this regard. Indeed, inspection methodologies that employ eddy current, acoustic, and other probe sensor technologies may also benefit from the teachings of the present disclosure.
The test objects for which these systems are used can be very long, e.g. 15 meters, with a wide range of diameters or cross sectional dimensions. For example, conventional pipe inspection systems can cover a range of diameters from 60 to 620 mm and wall thicknesses ranging from 4 to 50 mm. Conventional solid bar inspection systems can cover a range of diameters from 8 to 250 mm. Accordingly, the industrial setting where these products are produced and inspected must provide substantial material handling capabilities, factory floor space and other equipment resources.
Conventional pipe inspection systems (PIS) usually comprise:                a) a transport mechanism to feed or place the test object to be inspected in the proper test location;        b) a plurality of phased-array test probe heads positioned along the test object's longitudinal axis for the purpose of sensor data acquisition at multiple incident angles, which probe heads are operable to be moved axially and coupled along said axis while the test object is rotated in an axially stationary position;        c) a couplant irrigation system to provide an ultrasonic coupling medium, such as water, in a laminar fashion interposed between the surface of the probe heads and the test object;        d) a means to correlate the inspection sensor data acquired with the location on the test object where the inspection measurement was made; and        e) a computerized system for motion control and data acquisition.        
A conventional bar inspection system (BIS) is comprised of most of the same elements of the PIS described above; however, they differ with respect to element “b)” in that the ‘plurality of test probe heads’ are instead disposed in a stationary manner to surround and be coupled to the perimeter of the test object while the test object is transported axially. Typically, two or more parallel plane probe head arrangements (cartridges) are used to provide maximum perimeter inspection coverage, each with a circumferential offset to cover the zone that the others do not.
It should be noted that the specific method utilized to supply the coupling medium, such as water, between the probe head and the surface to be inspected varies from system to system, such as UT, PIS and BIS. Specifically, a PIS employs a continuous local stream of water with laminar flow for each probe head, whereas a BIS employs a large tank of water in which the probe heads and the region of the test object to be inspected are submerged together. Furthermore, an entry and exit hole is placed on the opposing sides of the tank for the test object to be axially transported therein. As expected, considerable challenges are posed by the need to seal the interface between the tank holes and the moving test object in order to minimize water leakage and maintain adequate water volume.
The water tank method is used instead of the probe head longitudinal axis transport method when the UT methodology is used in line with another stationary inspection methodology, such as EC inspection. In this case, the test object is axially transported through the closely positioned and stationary UT and EC inspection systems, spending a portion of the test cycle time in both. Accordingly, this presents a practical limitation on axial movement of inspection probe heads.
Notable drawbacks associated with the conventional PIS can be attributed to the following characteristics of PIS systems.
a) Substantial and precise motion control requirements are placed on the system mechanics due to the need to transport and rotate large and heavy test objects, and transport major portions of the test system as well. These requirements demand a high initial investment, increased maintenance costs, greater design and assembly complexity, produce occasional performance anomalies (such as encoder slippage), large power consumption, and overall equipment wear and tear. There are also production delays associated to loading the test object on the inspection conveyor.b) Adequate inspection coverage of the test object surface requires probe sensors operable to produce a plurality of incident inspection angles to deal with the fact that a flaw, such as a crack, may be orientated in the blind spot of a particular probe.
Accordingly, provisions must be made to ensure that each point on the outer surface of the inspected object is capable of being coupled to either: i) one probe with the ability to operate dynamically with multiple incident angles and/or apertures and/or ii) a large plurality of probes disposed in such a way as to achieve the same end.
The drawback associated with expedient ‘i’ above is that the motion of the test object has to stop, or be substantially slowed, to ensure that the probe couples the programmed range of incident angles at each point required on the inspected surface. Furthermore, the pulse repetition frequency (PRF) and speed of the data acquisition system needs to be quite high to ensure that the inspection throughput is not further compromised. Conversely, the inspection throughput can be increased, but only at the expense of reduced of inspection coverage, which results in lower inspection quality.
The drawback associated with expedient ‘ii’ above as compared to expedient ‘i’ above is primarily due to a large number of probes needed which require considerably more space due to the need for additional motion control apparatus and data acquisition units (DAU's). Furthermore, effecting motion control of the probes and the DAU's electronic enclosures is quite complex, including the need for cable management of probes, power, and external communications.
The most significant drawbacks associated with a conventional BIS are the same as those described above for the PIS, except that the test object is typically not rotated during inspection and the problems described above associated with the use of a water coupling tank are present.
Attempts to overcome the aforementioned drawbacks are exemplified by the teachings of U.S. Pat. No. 7,293,461 (Girndt) and U.S. Pat. No. 5,007,291 (Walters et al), both of which are summarized as follows.
Girndt teaches a method for ultrasonic inspection of tubular objects with a fixed set of parallel stationary circular arrays of composite transducers disposed and oriented to achieve thorough inspection coverage for the detection of anomalies, such as transverse, wall or longitudinal defects. To this end, Girndt employs composite transducers, which provide inspection area coverage greater than achievable with the same number of conventional non-composite transducers. Because many more non-composite transducers are required to cover the same area, the use of Girndt's arrangement of composite transducers reduces the number of channels needed for inspection of the tubular. More specifically, the primary advantages of composite transducer piezoelectric crystal material as compared to the conventional non-composite variety are: a) its face can be formed into a cylindrical or spherical shape that allows the UT beam to be focused without the need for an additional lens in front of the crystal face, and b) it provides a much higher excitation acoustic pulse for a given drive voltage which significantly improves the signal to noise ratio of the received echo.
The most significant drawbacks of Girndt's method involve a large number of transducers required for good inspection coverage as compared to a rotating probe system described below, and the difficulty to adapt to a wide range of test object diameters and wall thicknesses using a fixed set of composite transducers. As one might expect, a large number of transducers substantially increases system cost and complexity due to the number of DAU channels for signal processing. Furthermore, considerable changeover time is required to adapt Girndt's inspection system from one type of tubular geometry to another, which is beyond the inspection capabilities of a given set of composite transducers. Production system down time results in considerable productivity loss for the test object manufacturer. Furthermore, the test object manufacturer must invest in a separate set of curved face transducers for each test object size they produce that cannot be tested with the first set.
Walters et al. (U.S. Pat. No. 5,007,291) teaches a method for ultrasonic inspection of pipes that overcomes several aspects of the aforementioned background arts. The disclosure's use of multiple pairs of transducers (i.e. probes) disposed in linear, axial array for transmitting in each of the longitudinal and plurality of oblique directions increases the scan coverage for each revolution of transducers and therefore reduces the time required for an inspection.
In order to overcome the drawbacks associated with connecting a large number of transducer signals between the rotating and stationary parts of the inspection system, Walters teaches summing the response signals from all transducers in a “bank”, prior to providing them in analog form via a slip ring connection to a stationary amplifier module. Walters employs a plurality of transducer banks, each set to a fixed inspection incident angle. The transducers within each bank are mounted at a fixed angle to couple the UT pulse with the test object surface at one of a longitudinal, transverse, normal or oblique angle. In some cases, the transducers contained in the banks are complementarily oriented to face in either the forward or reverse clockwise rotational direction to maximize inspection coverage.
Although Walters' teachings overcome many of the aforementioned drawbacks of the background art, it falls short of providing easily and dynamically set, and wide variety of incident inspection angles and focal depths of the probe banks. In addition, as can be readily appreciated by those skilled in the art, the use of a slip ring connection for analog transducer signals poses problems associated with signal noise, limited bandwidth and a limited number of signal connections.
A review of the prior art can therefore be summarized that conventional ultrasound inspection systems as well as phased-array test object rotating inspection systems both have limitations in terms of the quality of the inspection, productivity, and cost effectiveness.
As phased-array technology is the current state of the art inspection method for performing full range inspection of test objects, it would therefore be beneficial to apply this technology to rotating head inspection systems thereby taking the advantages of providing inspections with higher resolution and higher through-put without the aforementioned disadvantages associated with conventional test object rotating system and rotating fixed incident angle probe inspection systems.
In view of the background art described above, a solution that more effectively addresses the noted drawbacks would be greatly appreciated by those in need of more efficient, reliable and cost effective inspection systems. The specific improvements required to accomplish this solution pertain to simplifying the motion control requirements for both the test object and inspection system, reducing the amount of floor space required for the system, allowing easy adaptation to a wide range of elongated test object sizes, and achieving optimal inspection performance by providing a means to allow a wide range of inspection probe incident angles and focal depths.